This invention relates to a printer and, more particularly, to a printer capable of having both a push-tractor type structure and a pull-tractor type structure.
Conventional printers were classified into either one of the pull-tractor type and the push-tractor type depending on the relationship between paper and a tractor.
Referring now to FIG. 1, a conventional pull-tractor type printer comprises a cylindrical platen 1 for supporting paper 3 from the rearside thereof to absorb the impact generated at the time of printing by a head 4, and a tractor 2 for pulling out the paper 3 from the platen. In this type of structure, however, since the paper is pulled by the tractor 2, the paper 3 cannot be cut at any location between the platen 1 and the tractor 2. For this reason, when a piece of paper 3 is cut out immediately after the printing, an operator must wait until the desired printed portion on the paper has passed through the tractor 2 to cut out said portion at a cutting position 8 behind the tractor 2. As a result, every time the paper is cut, the length of paper equal to the distance between the head 4 and the tractor 2 is inevitably wasted.
Referring to FIG. 2, a conventional push-tractor type printer comprises a platen 1 and a tractor 2 for feeding paper 3 to the platen 1. However, this type of structure is not suitable for multiple paper, which is composed of several sheets of paper stacked. As shown in FIG. 3, when multiple paper 10 is used, as the rotational radius of the inner side paper 11 close to the platen 1 is slightly shorter than that of the outer side paper 12 of the paper 10, the amount of feed of the paper 11 becomes smaller than that of the paper 12. This difference in the amount of feed causes a slack 13 of the paper 11. As the multiple paper 10 is continuously fed, the amount of the slack 13 increases and the slack 13 gradually accumulates large enough to jam. As a result, the feed of the paper 10 eventually becomes impossible. Such a conventional pull-tractor type printer is disclosed in the U.S. Pat. No. 4,344,715.
One object of the present invention is, therefore, to provide a printer free from the above-mentioned disadvantages of the prior art and capable of achieving both the pull-tractor and push-tractor type structures.